1. Field of the Invention
The present invention relates to a film-type electrostatic capacitance sensor for detecting seat occupancy, and more specifically to a film-type electrostatic capacitance sensor for reducing discomfort to an occupant.
2. Description of Related Art
As shown in FIG. 8 of the drawings, a 2-electrode film-type electrostatic capacitance sensor has been proposed which electrostatically detects whether a seat is occupied through two electrode layers 110 and 120 provided on both sides of a resin film 100 embedded in the seat. In the 2-electrode film-type electrostatic capacitance sensor, cover films 150 and 160 are bonded to the electrode layers 110 and 120 provided on both sides of the resin film 100 via adhesive layers 130 and 140 to cover and protect the electrode layers 110 and 120.
For the 2-electrode film-type electrostatic capacitance sensor, various configurations can be considered. For example, in JP-2001-201129 A, a film-type electrostatic capacitance sensor is proposed that applies an alternating voltage between one electrode layer and a vehicle body, supplies an alternating current to the other electrode layer to adjust the potential at the other electrode layer to a value equal to that of the potential at the one electrode layer, and determines whether a seat is occupied based on a change in the alternating current.
However, some difficulties arise with the above noted sensor configurations. For example, in accordance with the film-type electrostatic capacitance sensor described in JP-2001-201129 A, a seat equipped with the described sensor feels more uncomfortable to a vehicle passenger than a seat without such a sensor. The discomfort is due to the configuration and consistency of the detecting portion of the film-type electrostatic capacitance sensor for detecting seat occupancy. The typical sensor can include a resin film laminate structure as described above, having a characteristic that a resistance to deformation thereof along the shape of, for example, the lower or lumbar region of the human back is accordingly high, resulting in discomfort when pressure from a vehicle passenger's body is applied thereto.
In addition, further difficulties arise in that, with regard to the conventional film-type electrostatic capacitance sensor, since the two electrodes are located at different positions in the thickness direction of the resin film, the action of connecting each of the electrodes to an IC terminal composing a circuit portion becomes difficult.